1. Field of the Invention
This invention relates to a tool for delaminating very thin layers and more particularly to a tool for delaminating holograms from substrates to which they are bonded.
2. Description of Related Art
The manufacture of holograms entails the use of materials which are sensitive to moisture and thus must be protected. Moreover, during exposure, the hologram must be held stationary to within a fraction of a wave length of the exposing light.
Thus, in practice, a material such as dichromated gelatine is laid down in a thin layer upon an ultra thin sheet of glass, typically 0.007 of an inch thick. This sheet of glass acts as a moisture shield for the finished hologram. The face of the glass opposite the gelatine layer is temporarily bonded to a relatively thick substrate with an adhesive such as UV curable photopolymers. With the hologram thus held stationary, it is exposed to a holographic beam to record a holographic image pattern in the gelatine. When the exposure is completed it is then necessary to remove the hologram comprising the layer of gelatine and the ultra thin layer of glass from the substrate. However, while the hologram is flexible, the glass tends to be very brittle and is easily cracked during such removal.
Heretofore the hologram has been manually removed by a skilled operator using a spatula-like blade of thin metal having a sharpened edge and a rounded corner. Typically this blade has been 0.002 of an inch thick. The operator thus worked the spatula into the bond line between the substrate and the glass to delaminate the hologram from the substrate by cracking the adhesive bond. This resulted in a chaotic cracking of the adhesive layer because of the non-uniform bonding strength of the adhesive. Moreover as the operator applied more pressure to the thin spatula blade, it tended to buckle thereby greatly increasing the chance that the thin glass would be cracked. Even skilled operators destroyed some of the holograms as a result of the cracking of the thin glass, especially during the initial debonding at the periphery of the hologram. On top of this, the delamination process was relatively slow, even for a skilled operator, which increased the probability that some moisture would be absorbed by the gelatine during this delamination step.
There has been an even greater probability of breaking the thin layer of glass when the gelatine has been etched back from the periphery of the micro glass as is the case when the gelatine is to be sealed from moisture when the hologram is installed in its ultimate end use such as a windshield. With the gelatine etched back from the periphery it no longer provides support for the thin glass during the initial debonding. Consequently even more of the holograms were destroyed, even by skilled operators, during the delamination step.
As a result, a hologram which was time consuming to produce was destroyed in one of the final processing steps.